Date of Award

Spring 5-10-2019

Level of Access

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Plant, Soil, and Environmental Sciences

Advisor

Ellen Mallory

Second Committee Member

M. Susan Erich

Third Committee Member

Jessica Leahy

Abstract

In the past decade, Maine has witnessed a steady rise in consumer demand for organic small grain products, accompanied by the swift creation of new businesses that cater to this demand, including bakeries, flour mills, malt houses, and distilleries. Maine’s farmers have been slower to respond; only a small percentage of the 40,000+ acres of oats and barley being grown in the state, for example, is certified organic (National Agricultural Statistics Service, 2012). Given this combination of land resources, infrastructure, and consumer demand, Maine has the potential to become a regional leader in organic small grain production. According to our region’s growers, one of the biggest hurdles associated with growing small grains organically is accessing reliable, affordable nitrogen fertility to support their crop systems. This thesis employs both quantitative, field-based methods and qualitative tools to help tackle this issue by exploring the use and management of legume green manures (LGMs) in production.

Chapter 1, “Alternative Methods for Terminating Green Manures in Organic Small Grain Systems,” describes a field experiment in Maine and Vermont that aimed to evaluate potential alternatives to the standard method of terminating LGMs in our region, moldboard plowing. This study assessed four different LGM termination methods for kill efficacy, winter soil cover, and N supply to a subsequent crop. Plowing resulted in the highest early season N uptake and grain crude protein in wheat at one site, though wheat yields were statistically similar among termination treatments at all but one site. We found that undercutting, as practiced in this trial, increased protective winter soil cover relative to moldboard plowing, but failed to adequately kill the LGM. Skim plowing, which uses the same implement as the standard method but involves less soil disturbance, increased soil cover relative to plowing at one site, and resulted in similar kill efficacy to plowing, making it a promising alternative.

Chapter 2, “Challenges, Strategies, and Research Priorities in Legume-Based Nitrogen Management for Organic Small Grain Producers in the Northeastern U.S.” describes a qualitative investigation of organic small grain farmers and agricultural advisors regarding issues encountered in general nitrogen management, and use of LGMs in particular. Through semi-structured interviews, farmers and advisors revealed major challenges to be cost, over-dependence on external nitrogen sources, diversifying rotations, weed management, and predicting nitrogen mineralization of organic residues. Market-based challenges, such as the cost of LGM seed and limited cash crop markets, represent significant barriers not easily solved through research and programming. This study highlights the need for on-farm, participatory research aimed at assessing potential alternatives to external nitrogen sources, addressing field-based challenges associated with LGMs, and bolstering grower confidence in legume-based nitrogen management.

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